Troubleshooting guide
Thermoforming defects & troubleshooting
Most thermoforming defects trace back to a handful of causes — heating, material distribution, tooling or cooling. This guide covers the common ones: what each looks like, why it happens, and how to fix and prevent it. Pick a defect below, or send us a sample and we'll diagnose it.
Heating
Sheet sagging
The heated sheet droops too much before it is formed.
Uneven heating
The sheet reaches forming temperature unevenly across its area.
Blisters & bubbles
Raised bubbles or blisters in the sheet surface after heating.
Scorching & burn marks
Discoloured, burnt or degraded areas from too much heat.
Forming
Webbing
Folds or pleats of excess material at corners and between tall, closely-spaced features.
Bridging
The sheet spans across a recess instead of forming down into it.
Wall thinning
Walls — especially in deep draws and corners — end up too thin.
Poor detail definition
Edges, text and fine features come out soft or rounded.
Vacuum leaks
The tool cannot hold enough vacuum to draw the sheet down fully.
Sheet & material
Blushing
Whitish haze or marks where the material was over-stretched.
Crazing & stress cracking
Fine cracks that appear under stress, chemicals or over time.
Colour streaks & shade variation
Streaks, marbling or batch-to-batch colour differences.
Brittleness & cracking
Parts crack or shatter instead of flexing under load or impact.
Black spots & specks
Small dark specks or spots scattered through the sheet and the formed part.
Cooling & trim
Warping
The part twists or distorts from its intended shape after forming.
Bowing
A large flat or shallow part curls along one axis.
Sink marks
Localised depressions on the surface, often opposite a thick spot or feature.
Orange peel
A rough, dimpled surface texture resembling orange skin.
Chill marks
Lines or marks where the hot sheet touched a cold surface too early.
Part sticking to the mould
The formed part will not release cleanly from the tool.
Nibs & mould mark-off
Small pimples or dimples from vacuum holes or tool debris.
Trimming burrs & rough edges
Rough, ragged or burred edges after trimming.
Shrinkage & dimensional drift
Parts finish smaller than the tool or drift out of tolerance.
Diagnose a problem
Seeing a defect we haven't listed?
Send a photo, drawing or sample — our engineers will identify the root cause and the tooling, material and process fix, usually within 24 hours.
ISO 9001:2015 certified · Most quotes back within 24 hours